1. Field of the Invention
The present invention relates to a capacitor in which internal electrodes are arranged in layers with a dielectric layer sandwiched between opposed internal electrodes. More particularly, the invention relates to a laminated capacitor or rather multilayer capacitor using via electrodes for electrically interconnecting individual terminal electrodes and internal electrodes.
2. Description of the Related Art
In a multilayer capacitor, first electrode layers and second electrode layers serve as the internal electrodes; the dielectric layer is sandwiched between the opposed first and second electrode layers; and a large number of via electrodes are provided so as to extend or rather penetrate through the dielectric layers in the laminating direction of the first and second electrode layers and electrically interconnect the first electrode layers and the second electrode layers, respectively (refer to, for example, Patent Documents 1 and 2 below). Such a multilayer capacitor is considered to be suitable for use as, for example, a decoupling capacitor for reducing power noise of an IC.
[Patent Document 1] Japanese Patent Laid-Open (kokai) No. 2002-359141
[Patent Document 1] Japanese Patent Laid-Open (kokai) No. 2003-158030
Such a capacitor must have high capacitance and low inductance. Generally, to meet this requirement, internal electrodes are arranged in layers. A single dielectric layer has a portion where an electrode is formed, and a portion where the electrode is not formed. Accordingly, when such dielectric layers are laminated in order to arrange the electrodes in layers, a thickness differential (electrode-induced thickness differential) or so called an electrode step (or an electrode height difference) arises in the capacitor between an electrode-containing portion and a portion not containing electrodes. In order to absorb such an electrode-induced thickness differential, a thick dielectric layer portion, which is generally called a “base layer,” is provided on the surface of the capacitor. In order to absorb the electrode-induced thickness differential, the base layer is formed relatively thick.
3. Problems to be Solved by the Invention
However, the above-mentioned conventional capacitor gives rise to the following problem.
In the above-mentioned multilayer capacitor having via electrodes, the via electrodes extend through the base layer and are electrically connected to the internal electrodes which underlie the base layer. Accordingly, each of the via electrodes includes a portion that extends across the thickness direction of the base layer and is not electrically connected to the internal electrodes.
In recent years, the processing speed of an IC used with a capacitor has increased, and thus a decoupling capacitor requires further reduction in inductance. However, inductance is increased by via electrodes each having a long portion that extends without being electrically connected to internal electrodes as mentioned above. Inductance increases with the thickness of the base layer. An increase in inductance hinders an improvement in electrical characteristics of the multilayer capacitor, particularly at high frequencies. Such a problem can be solved or suppressed by reducing the thickness of the base layer. However, reduction in the thickness of the base layer is limited, in view of the above-mentioned absorption of electrode-induced thickness differential. Therefore, reducing the thickness of the base layer is not a practical solution.